1. Isotherm Study of Metal Ion Adsorption onto Tree Fern
Chung-Chi Wang* and Yuh-Shan Ho#
School of Public Health, Taipei Medical University
Introduction
Adsorption has been an effective separation process for a wide variety of applications. Various agricultural products and by-products have been investigated to remove metal ions from wastewaters. In this study, the adsorption capacity of tree fern for cadmium and mercury ions has been investigated by determining the equilibrium isotherm. The system variables studied include adsorbent particle size and temperature. In each system the isotherm constants for the Langmuir (1916), Freundlich (1906) and Redlich-Peterson (1959) isotherms have been determined.
Materials and Methods
The raw tree fern was dried in an oven at 105°C for a period of 24 h. The adsorbent was screened to get different geometrical sizes such as 44-53, 53-61, 61-74, 74-88, and µm. The stock solutions of cadmium ions (650 mg/dm3) and mercury ions (1000 mg/dm3) were prepared in distilled water.
Batch adsorption experiments were conducted at a constant speed of 100 rpm in a shaking water bath using 125 ml conical flasks with temperatures of 10, 15, 20, 25, 30 and 35°C, respectively. In all sets of experiments, 0.2 g of tree fern was thoroughly mixed into 50 ml ions solution. After shaking the flasks for 12 h, the tree fern was separated by centrifugation (3000 rpm, 10 min). The filtrate was analysed for the remaining ions concentration by using inductively coupled plasma atomic emission spectroscopy analyser (ICP-AES).
Results and Discussion
Equilibrium relationships between adsorbent and adsorbate are described by adsorption isotherms, usually the ratio between the quantity adsorbed and that remaining in the solution at a fixed temperature at equilibrium. In order to investigate the adsorption isotherm, three equilibrium models were analyzed. These included the Langmuir, the Freundlich and the Redlich-Peterson isotherms.
Table 1. Isotherms and their linear forms
Table 2. Adsorption isotherm constants for the Cd and Hg ions at various temperatures
Figure 1. Isotherms for the adsorption of Cd and Hg ions using tree fern at various temperatures
Figure 2: Isotherms for the adsorption of Cd and Hg using tree fern
Conclusion
Tree fern is a suitable adsorbent for the removal of cadmium and mercury from aqueous solution.
Both Langmuir and Redlich-Peterson isotherm provides the best fit for the adsorption of the cadmium and mercury ions on tree fern.
Adsorption is an endothermic process, it would be expected that an increased solution temperature would result in a increased adsorption capacity.
The adsorption capacity of mercury is higher than that of cadmium.
References
Langmuir, I. (1916), The constitution and fundamental properties of solids and liquids. Journal of the American Chemical Society, 38,
Freundlich, H.M.F. (1906), Über die adsorption in lösungen. Zeitschrift für Physikalische Chemie, 57,
Redlich, O. and Peterson, D.L. (1959), A useful adsorption isotherm. Journal of Physical Chemistry, 63, 1024.